Tuesday, October 29, 2013

Air source, Ground Exchange, GSHP, MVHR discussion

29 Oct 2013: Continuing the conversation, David R writes: "With the DHSS and some iterations of the Viking House solar/passive slab the earth store is insulated from the fabric of the building but is continuous at its base to the surrounding earth which would hopefully mitigate most of the effects you describe.
      Of greater concern to me is the size needed for effective storage; our build is a super insulated triple-glazed SIPS structure which should have relatively low space heating requirements with MVHR. On the Viking House site they indicate that some of their stores are sized sufficiently to cover the required number of heating days for the thermal load of the building, I was just not sure how accurate that would be?
   Thanks for the info re the boreholes, four shallow ones would certainly seem to be a way around the problem. Do you know how GSHP compares to ASHP in terms of power requirement? That seems to be one of the issues we have for our SAP calculations in that we need a load of PV to offset the heat-pump usage.
     As an aside re ASHP, for our MVHR unit we are installing a Rehau EcoAir Ground to air heat exchanger to pre-heat (or cool) supply fresh air to the MVHR. As ASHP seem to have a significant power penalty and COP loss due to de-icing during winter why do none of them allow for such a simple pre-heat fix as a ground buried supply pipe?"

David N-C replied same day: I don't have a comparable consumption figure for the ASHP although there is data on the web, e.g., the Mitsubishi Ecodan brochure shows useful information. We have one in one of the ecohouses on the campus here, but i enquired and nobody is keeping metering records for it…. so what is the point. Its lived in by PhD students who could be keeping records!!
     If the store under your Viking house is uninsulated downwards, I would merely have about a metre down drop of perimeter insulation, and let the underside of the store reach down to the infinite everywhere below. Perimeter losses are very seasonal and wasteful. Is the footprint of the house sufficient? Mine is two storey, with a footprint of only 9.6x7.2m2…. If the pipes below are unjointed and made of ground loop or borehole rugged plastic, then there is better security against fracture. They should still be buried as deep as you are willing to go. If you are actively solar charging the store, you can protect against a frost heave, and if the occupant (you and successors) have a temperature sensor in the store, you can turn the solar charging off if you have an extremely hot summer and are worried about over heating.
     Ground to air exchange is a good passive method for pre tempering your MVHR air and Rehau are the best experts in it, including the means of dealing with health risks etc. That will be around the perimeter? I have an undercroft below this house, and should have thought of using that as an air intake if we had a whole house MVHR fitted.
     An ASHP is a closed box in that it is not designed to be adaptable. A GSHP is really a general purpose device that could be adapted by being linked to solar panels, air to air exchanger or ground boreholes. the one we have included the water tank, so is inside the house, to shorten pipe runs.
     The reason that ASHP doesn't use ground air exchange is that the airflow rate is many times that of MVHR. The flow rate would be so fast that there wouldn't be time for a heat transfer, whereas the MVHR only requires 0.6 ac/hr. Actually, I have just done a calculation and that seems quite a lot of air! For my house of 600 cubic metres, that means 360 cubic metres of change, which is 6000 litres/minute or 100 litres per second…. which has to be reheated by the MVHR.
    An ASHP is flowing 50-100 cubic metres/minute of air through its fan depending on size. Taking 50 for a house with excellent insulation, that would be 833 litres per second. A larger model would use twice that amount. It needs to draw the air from the infinite everywhere and not be hampered by the frictional losses of a pipe with an air intake big enough for children and animals to get lost in!

PS, to most people DHSS is the Department of Health and Social Security... only a few thousand google hits before finding the one you mean!

David R replies: "Thanks for all your input... We have a bigger footprint (around 115m2) but I can still see this being marginal for an effective heat store unless the pipes are trenched in at some depth, which has its own health and safety issues. I think I will try to get some comparative costs for what would be needed as a sub-foundation store compared to a borehole scenario.
    With respect to using ground air heating to pre-heat an ASHP, I had suspected the flow rates would be the issue and your reply certainly puts that into perspective.... I think the badgers have a surfeit of available habitat around here without adding more artificially!
     I will let you know how things pan out, thanks again for your consideration!"

Monday, October 28, 2013

Enquiry about putting thermal energy UNDER the house

28 Oct 2013: David R writes: "I read with interest your blog posts as we are currently attempting to build a code 5 / 6 property in Northumberland, albeit somewhat remotely as we currently live in sunnier climes!
    I have been intrigued for a long time about the use of soil for inter-seasonal heat storage and followed the Viking House iterations in Ireland with interest. Your own endeavours with solar recharging of the boreholes seems to be a similar concept.
    As we are soon to break ground we really have to decide on the most appropriate (and affordable) technology and I am still looking along the lines of a below house thermal store. I saw you posted a link to the DHSS site and I have had some communication with them about their product, but they seem to be suggesting a huge amount of solar thermal tubes to dump heat below the building structure. We are already committed to a Viking House style passive slab for the foundation with 300mm of EPS insulation, so we could easily look at installing a thermal soil store beneath the foundations but my own grasp of the physics involved isn't good enough for me to work out if this would actually work in reality and whether the house footprint would be sufficient for a GSHP in this recharging scenario.
     I wondered if you had any thoughts on this DHSS type of set-up?"

David N-C replied same day: Thanks for reminding me of the Viking House. Very impressive. My project started with an existing house, so could not bury energy literally under the house and the idea started with thinking of a Future house under which we would do what you are thinking of :- putting solar energy under the house with a very well insulated floor slab to contain it. A few problems with that:
  • If you make the store insulated, its as expensive as building yourself an earth filled swimming pool (without the pleasure) and couldn't be big enough to meet the needs of a whole house. it would be well freezing by the end of Feb!
  • The house could need a volume of solid soil larger than the house itself if you have it enclosed with insulation.If it is smaller, you need to build up to a higher temperature, and cool down to a lower.
  • House could be designed to span structurally across the slab area so that shrinkage or swelling are not a problem, but this is expensive.
  • You must never allow the store to swell with frost heave. When the store reaches below 4degs, it might be moving to a point where it expands after it gets cooler - lifting the house! GSHPs can go below 4degs. You should avoid putting so much heat into it so that it becomes like a hard rock with large shrinkage cracks which tear your pipes apart and require abandonment when leaks occur - or which cause house to settle.
  • If it is uninsulated (like a borehole), this is safer, as the store has 'infinite' size and pulls energy in from outside in the cold spring months to stop it freezing. It is safer against overheating as the outside mass will stabilise it by allowing surplus heat to leak out.
  • For those reasons, we reason that vertical boreholes... comparatively easy and quick to drill... NEXT to the house.... are the best option, provided the soil below is right. Infinite size, no risk to the foundations, minimal seasonal heat loss, minimum cost, minimum land. Four shallow ones are better than one deep one if you include solar charging.

October 2013 Reports

27 Oct 2013: (Just remembered, it's my mother's birthday... ) Sebastian Vettel won the Formula One championship, Lou Reed died, and Britain braced itself for a hurricane. Angela Merkel complained about the Americans having bugged her private phone for over a decade. The biggest talking point of the news is the hike in energy prices by the Big Six, and by them blaming it on green 'levies' and then Cameron completely siding with them and demanding a roll-back of the green levies the largest proportion of which he has applied since 2010. The greenest government ever was a lying electoral slogan.
    On Peveril Solar house, we still have this agonising 32 kWh between the PV and the GSHP consumption (triennial figures), but this is closing slowly - its equal to 3.6watts, an LED lightbulb left on for the year. The GSHP consumption includes hot water, so for heating, we are well into credit.
  • House annual 5,316, biennial 5,285 kWh. Reducing.
  • GSHP annual 3,229, biennial 3,227 kWh, triennial 3,209 kWh. Reducing. 
  • PV annual 3,080, biennial 3,058 kWh, triennial 3,177 kWh. No change.... 
  • Sunbox annual 3,366, biennial 2,901 kWh. One up, one down....
  • Ground Temperature 13.1ºC. Amazing...still above 13!
20 Oct 2013: Its been a week of cold and rainy weather. No figures this week.... but the weekend was sunny, so the end of week Ground Temperature was 13.1ºC - a brief twitch of the summer, before it finally gets really cold. The last beans were picked, and the courgette plants are still producing vegetables!
    In the world outside, the US government shut down ended - at a huge cost to the US economy, and with not a cent being deducted from the salaries or the perks enjoyed by the Republican congress men who caused it.

13 Oct 2013: We've had a whole week of overcast weather, with a lot of drizzly rain. As the same thing was happening a year ago, things are pretty stable. The heating is on every day now, and my wife expects it to be on, warm. We cannot sit around shivering in woolly pullovers trying to improve my metering figures.
  • House annual 5,373, biennial 5,282 kWh. Steady.
  • GSHP annual 3,301, biennial 3,243 kWh, triennial 3,233 kWh. Reducing. 
  • PV annual 3,080, biennial 3,075 kWh, triennial 3,175 kWh. Reduced... 
  • Sunbox annual 3,323, biennial 2,921 kWh. No change
  • Ground Temperature 12.5ºC. Now going into winter mode.

Friday, October 18, 2013

Lecture to CIBSE North West

17 October 2013: I was invited by the CIBSE North West branch to do a longer version of my lecture about the Peveril Solar House. This was held at Blundell Hills golf club in Rainhill (closer than Liverpool, but requiring me to drive in the car). I completely forgot to take a photo, but here's a screen shot of one of the PPT pages. According to Steve, the organiser, it was a larger turnout than usual, but I put that down to the excellent preview he provided for the lecture in his website!
Click the image below to get a PDF of the lecture.

Thursday, October 10, 2013

Second PV array to feed electric car

11 Oct 2013: Somebody called Trevor wrote a comment on an earlier posting of mine and he has directed me to an interesting blog about his electric Renault Zoe car. (I don't care if he works for Renault, the posting is about installing PV).
He has PV fitted in 2010, and that is the usual grid connected system with the Feed in Tariff. He has recently added extra panels on the north roof, because the 2010 system took up his entire south roof. He has kept solar generating metering records since the start, and house electricity records since 2008. It isn't clear if the second PV panel array is added to the original 3.7kW system as a grid connected system, because as far as I know, this would alter the terms of his original F.I.T agreement.
As the blog is mostly about the electric car, I guess that this is to reduce his small running cost of the car.

Wednesday, October 9, 2013

PV on a Train station

I heard about this project frmoAlex Mungo of Eco Kinetics, St Albans.
Eco-Kinetics specialize in installing Solar PV Systems, Solar Energy, Solar Panels and Solar Power systems for residential and commercial entities. They were recently successful in winning a tender for the installation of a trial system at one of Network Rail’s maintenance depots, which along with other energy reduction measures will help to reduce energy costs and carbon emissions at the site.
With a tilt frame mounting, and some active decisions to modify the angles every couple of months, this should be an efficient system. 

Digital Self Heating Homes

9 Oct 2013: More detail will be added about http://www.dshh.info/

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